Stern-mounted hydrofoil device



April 29, 1958 D. A. ELYOSIUS ET AL 2,332,304 STERN-MOUNTED HYDROFOIL DEVICE Filed Aug. 50, 1955 INVENTORS United States Patent 2,832,304 STERN-MOUNTED uvnzaoron. DEVICE Donald A. Elyosius and Peter V. Elyosius, Hartford, Conn.

Application August 30, 1955, Serial No. 531,488

1 Claim. (Cl. 114--66.5)

This invention relates to a marine device providing a hydrofoil element of high lift to drag ratio supported by a strut-and-bracket assembly to be mounted on the stern of a waterborne hull.

The usefulness of this invention arises from the fact that certain hulls of various hydrodynamic efiiciencies, whether of the planing or displacement type, under some conditions of loading or power, are characterized by a common defect of performance resulting from improper hull-attitude, said hulls riding with bow excessively elevated and stern excessively depressed.

Undesirable consequences of this hull-attitude include: speed reduction due to increased underwater profile drag; speed reduction and increased rough-water pounding due to the broad hull-bottom being forced to serve in place of the lean, forward entering-sections of the bow; impaired course-holding ability, impaired control while maneuvering and increased pitching in rough water due to shorter, immersed hull-length; impaired visibility for ward due to excessively elevated how.

The primary object of this invention is to provide a hydrofoil element of high lift to drag ratio so mounted and so positioned as to apply a lifting force to the stern of a hull of the type described, thus correcting said improper hull-attitude and eliminating the attendant undesirable consequences thereof.

Another object of this invention is to provide a means of adjustment for said hydrofoil element to permit control of said lifting force by varying the angle of attack of the foil.

A further object of this invention is to provide a hydrofoil device, the lateral extension of the foil being limited so as not to project beyond the sides of the hull, thus permitting unhampered dock-approach and other close maneuvering.

A further object of this invention is to provide a hydrofoil device so constructed as to permit mounting while afloat and without structural alteration of said hull.

structurally, prior art has employed foil elements extending outboard of the hull sides with lift forces longitudinally and laterally distributed so as to permit a stable emergence of the entire hull, or it has employed fins so constructed as to permit reduction of short-term pitching or rolling movements of the hull, or it has employed structures requiring special hull forms or extensive modification of existing hulls or their fittings.

This invention is continuous in its action underway, the foil element remaining constantly submerged, the lifting force being confined approximately to a single transverse vertical plane well aft of the center of gravity, said lifting force aiding but not usurping the normal hull-functions of support and stability.

With the foregoing and other objects in view, this invention resides in the novel arrangement and combination of parts and in the details of construction hereinafter described and claimed, it being understood that changes in the precise embodiment of the invention herein described may be made within the scope of what is claimed without departing from the spirit of the invention.

A simple embodiment of this invention, selected for presentation because it represents the results of successful experimentation, is shown in the accompanying drawing in which:

Figure l is a perspective view showing the hydrofoil device, constructed according to the principles of our invention, attached to the transom of a typical inboardpowered, twenty-foot cruiser.

Figure 2 is a side view in elevation showing the port outboard strut attached to the end of the foil.

Figure 3 is a side view in elevation showing one of the mounting brackets.

Referring particularly to Figure 1, the port foil half 1 and starboard foil half 2 are shown in the position atfording minimum lift attached to the lower ends of struts 4 and 5 which are pivotally attached at their upper ends by bolts 14 and locked in position by bolts 15 to the brackets 6 which are mounted on the transom 3 of the boat.

Space to permit free movement of the rudder 16 is provided by the foil element being divided into two halves 1 and 2, each half being inclined laterally to form a dihedral angle and limited in lateral extension so as not to project beyond the sides of the boat. Since use of the device results in some reduction of hull-displacement underway and a consequent slight reduction in metacentric height, said dihedral angle is made sufficiently acute to provide a degree of dynamic stability more than sufficient to compensate for any stability loss in the hull. The entire foil element is positioned athwartship somewhat aft and below the lower edge of the transom 3 to insure submergence of the foils yet not so low as to increase the maximum draft of the boat.

The foil element is shaped in section to obtain high lift to drag ratio at the contemplated speed, aspect ratio being a secondary consideration in view of the aforementioned limitation on lateral extension but being made as large as possible within such limitation. Although variable, the angle of attack of the foil element is maintained at a positive value in all positions within the range of adjustment.

The outboard ends of the foils are attached to struts 4 which (viewed from astern) rise vertically and are bolted to the outboard brackets 6. The inboard ends of the foils are attached to struts 5 which (viewed from astern) rise vertically to a point slightly higher than the bottom of the boat, curve inboard, then rise vertically again to bolt to the center bracket 6. Except for the aforementioned curves and additional length, inboard struts 5 are identical with outboard struts 4.

As shown in Figure 2, strut 4 has near its upper end a hole 7 and intermediate this hole and the lower end of said strut, at a point higher than the bottom of the boat, another hole 8. Each strut is rectangular in section, presenting a thin edge fore and aft to reduce drag, and is sufliciently rigid to withstand without bending or undue vibration the lift and drag forces impressed on it by the attached foil.

The outboard and center brackets 6 are identical, consisting of a rectangular mounting plate which has midway its sides a perpendicularly projecting adjustment plate of the form shown in Figure 3. As seen in Figure 3, this adjustment plate has near its upper end a hole 9 corresponding to hole 7 in the strut. Below this hole are three additional holes 1t), 11 and 12 with centers lying on an arc whose center is the center of hole 9 and whose radius is equal to the distance between centers of holes 7 and 8 on strut 4.

Referring again to Figure .1, the brackets 6 are attached to the transom 3 of the boat with their lower edges adjacent to the waterline 13. This permits attachment of the device while the boat is afloat.

Corresponding holes of each bracket are in vertical and horizonal register and holes 9 are in register with the upper strut holes 7 permitting pivot bolts 14 to act as hinge pins thus allowing the lower end of the strut and foil assembly to swing fore and aft varying the angle of attack of the foils. Accordingly hole 8 on the struts may be brought successively into register with holes 16. 11 and 12 on the brackets and held in the chosen position by locking bolts 15. The range of adjustment so provided is sufficient to permit satisfactory operation.

While the device is intended to bring the boat to a nearly level position, the optimum position is one in which the bow is allowed to maintain a somewhat elevated attitude. Excessive lift, due to too great an angle of attack, can actually cause the boat to ride with a bowdown attitude.

In use, the foil is first set at minimum angle of attack, as shown in Figure 1, and performance checked. The precise degree of attitude-correction required is an individual matter subject to the choice of the operator.

With optimum adjustment, the bow remains sufliciently elevated to provide reserve bouyancy yet is sufficiently depressed to permit its sharper entering-sections to be effective in minimizing pounding in rough water as well as a noticeable increase in speed, such increase being the result both of the improved entering characteristics and a reduction in the angle of attack of the boats bottom surfaces. Such adjustment is achieved by increasing the angle of attack of the foil element a step at a time, checking performance at each step. The optimum position is not critical, however, and, once determined, allows considerable variation in speed and loading without further adjustment.

t should be understood that the invention as shown and described in the foregoing represents but one of several possible embodiments. The division of the foil elements into separate halves, for instance, is not an essential feature of theinvention. Also, it is understood that each separate foil half may be supported by a single strut, and

the method of adjustment may be altered to provide a greater range or finer degree of adjustment and may even include a source of power to facilitate such adjustment.

Nor is the application of the invention limited to the type of boat shown and described in the foregoing specification, it being equally applicable to all types of watercraft and waterborne aircraft exhibiting the aforesaid undesirable performance characteristics.

What :claim is:

A de its, including cambered hydrofoil means affixed to the lower end of a strut, the upper end of said strut being pivotally attached to a bracket which is attached to the transom of a boat above the Waterline of said boat, said bracket being the sole means of attachment of said device to said boat, said strut and bracket including a means of adjustment to permit varying the inclination of said strut thus varying the angle of attack of said hydrofoil means, said hydrofoil means being maintained in a constantly submerged position aft of and below the lower edge of said transom, said hydrofoil means including a dihedral angle and having a total span approximately equal to the beam of said boat, said hydrofoil means including port and starboard segments independently mounted to permit choice of dihedral angle at time of installation and independently adjustable to permit control of attitude of said boat about its longitudinal axis, said device being capable of developing suflicient hydrodynamic lift to raise the stern of said boat.

References Cited in the file of this patent UNITED STATES PATENTS 1,038,226 Hewitt Feb. 24, 1914 1,187,268 Crocco June 13, 1916 1,355,736 Curtiss Oct. 12, 1920 1,723,577 Rebl Aug. 6, 1929 2,081,868 Hampden May 25, 1937 FOREIGN PATENTS 1,563 Great Britain of 1892 547,951 Germany Apr. 8, 193.2 

